The objective of the proposed research is to develop a reliable, real-time feedback control technique for the precise, automated control of optimal light doses during photocoagulation therapy of the retina. The specific aims are to design and develop instrumentation and arrive at a computerized algorithm that utilizes induced dynamic changes in tissue reflectance to rapidly monitor and control the degree of coagulation achieved. The principle of such a diagnostic concept for retinal photocoagulation has already been demonstrated in the scientific literature. The goals of the proposed Phase I studies are to: (1) design an electro-optic reflectance measurement instrument that will work under a wide variety of realistic clinical conditions, i.e., various beam access geometries an diverse optical conditions in the eye, (2) perform preliminary testing of this instrument in a simplified laboratory eye model, and (3) devise a preliminary design of a signal processing and beam control system (hardware and software) that will utilize the optical feedback signal to control the laser delivery parameters (power and exposure duration). Subsequent Phase II studies would involve assembling and testing a prototype device and employing this instrumentation in a series of clinical photocoagulation procedures performed on rabbits. Efforts would also be made in Phase II to collect preliminary reflectometry data during selected human procedures.